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FreeBSD-SA-08:03.sendfile                                   Security Advisory
                                                          The FreeBSD Project

Topic:          sendfile(2) write-only file permission bypass

Category:       core
Module:         sys_kern
Announced:      2008-02-14
Credits:        Kostik Belousov
Affects:        All supported versions of FreeBSD
Corrected:      2008-02-14 11:45:00 UTC (RELENG_7, 7.0-PRERELEASE)
                2008-02-14 11:45:41 UTC (RELENG_7_0, 7.0-RELEASE)
                2008-02-14 11:46:08 UTC (RELENG_6, 6.3-STABLE)
                2008-02-14 11:46:41 UTC (RELENG_6_3, 6.3-RELEASE-p1)
                2008-02-14 11:47:06 UTC (RELENG_6_2, 6.2-RELEASE-p11)
                2008-02-14 11:47:39 UTC (RELENG_6_1, 6.1-RELEASE-p23)
                2008-02-14 11:49:39 UTC (RELENG_5, 5.5-STABLE)
                2008-02-14 11:50:28 UTC (RELENG_5_5, 5.5-RELEASE-p19)
CVE Name:       CVE-2008-0777

For general information regarding FreeBSD Security Advisories,
including descriptions of the fields above, security branches, and the
following sections, please visit <URL:http://security.FreeBSD.org/>.

I.   Background

The sendfile(2) system call allows a server application (such as a
HTTP or FTP server) to transmit the contents of a file over a network
connection without first copying it to application memory.  High
performance servers such as the Apache HTTP Server and ftpd use sendfile.

II.  Problem Description

When a process opens a file (and other file system objects, such as
directories), it specifies access flags indicating its intent to read,
write, or perform other operations.  These flags are checked against
file system permissions, and then stored in the resulting file
descriptor to validate future operations against.

The sendfile(2) system call does not check the file descriptor access
flags before sending data from a file.

III. Impact

If a file is write-only, a user process can open the file and use
sendfile to send the content of the file over a socket, even though the
user does not have read access to the file, resulting in possible
disclosure of sensitive information.

IV.  Workaround

No workaround is available, but systems are only vulnerable if
write-only files exist, which are not widely used.

V.   Solution

Perform one of the following:

1) Upgrade your vulnerable system to 5-STABLE, 6-STABLE, or
7.0-PRERELEASE, or to the RELENG_7_0, RELENG_6_3, RELENG_6_2,
RELENG_6_1, or RELENG_5_5 security branch dated after the correction
date.

2) To patch your present system:

The following patches have been verified to apply to FreeBSD 5.5, 6.1,
6.2, 6.3, and 7.0 systems.

a) Download the relevant patch from the location below, and verify the
detached PGP signature using your PGP utility.

[FreeBSD 6.2, 6.3, and 7.0]
# fetch http://security.FreeBSD.org/patches/SA-08:03/sendfile.patch
# fetch http://security.FreeBSD.org/patches/SA-08:03/sendfile.patch.asc

[FreeBSD 6.1]
# fetch http://security.FreeBSD.org/patches/SA-08:03/sendfile61.patch
# fetch http://security.FreeBSD.org/patches/SA-08:03/sendfile61.patch.asc

[FreeBSD 5.5]
# fetch http://security.FreeBSD.org/patches/SA-08:03/sendfile55.patch
# fetch http://security.FreeBSD.org/patches/SA-08:03/sendfile55.patch.asc

b) Apply the patch.

# cd /usr/src
# patch < /path/to/patch

c) Recompile your kernel as described in
<URL:http://www.FreeBSD.org/handbook/kernelconfig.html> and reboot the
system.

VI.  Correction details

The following list contains the revision numbers of each file that was
corrected in FreeBSD.

Branch                                                           Revision
  Path
- -------------------------------------------------------------------------
RELENG_5
  src/sys/kern/kern_descrip.c                                  1.243.2.11
RELENG_5_5
  src/UPDATING                                            1.342.2.35.2.20
  src/sys/conf/newvers.sh                                  1.62.2.21.2.21
  src/sys/kern/kern_descrip.c                               1.243.2.9.2.1
RELENG_6
  src/sys/kern/kern_descrip.c                                  1.279.2.16
  src/sys/kern/uipc_syscalls.c                                  1.221.2.5
RELENG_6_3
  src/UPDATING                                             1.416.2.37.2.5
  src/sys/conf/newvers.sh                                   1.69.2.15.2.4
  src/sys/kern/kern_descrip.c                              1.279.2.15.2.1
  src/sys/kern/uipc_syscalls.c                              1.221.2.4.4.1
RELENG_6_2
  src/UPDATING                                            1.416.2.29.2.15
  src/sys/conf/newvers.sh                                  1.69.2.13.2.14
  src/sys/kern/kern_descrip.c                               1.279.2.9.2.1
  src/sys/kern/uipc_syscalls.c                              1.221.2.4.2.1
RELENG_6_1
  src/UPDATING                                            1.416.2.22.2.26
  src/sys/conf/newvers.sh                                  1.69.2.11.2.25
  src/sys/kern/kern_descrip.c                               1.279.2.6.2.1
  src/sys/kern/uipc_syscalls.c                              1.221.2.1.2.1
RELENG_7
  src/sys/kern/kern_descrip.c                                   1.313.2.1
  src/sys/kern/uipc_syscalls.c                                  1.259.2.2
RELENG_7_0
  src/UPDATING                                              1.507.2.3.2.3
  src/sys/kern/kern_descrip.c                                   1.313.4.1
  src/sys/kern/uipc_syscalls.c                                  1.259.4.2
- -------------------------------------------------------------------------

VII. References

http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2008-0777

The latest revision of this advisory is available at
http://security.FreeBSD.org/advisories/FreeBSD-SA-08:03.sendfile.asc
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